Preheater and vaporizer for gas turbine engines



Jan. 5, 1954 w. B. WHITELAW 03 PREHEATER AND VAPORIZER FOR GAS TURBINEENGINES 2 Sheets-Sheet 1 Filed June 24, 1950 Jan. 5, 1954 Filed June 24,1950 W- B. WHITELAW PREHEATER AND VAPORIZER FOR GAS TURBINE ENGINES 2Sheets-Sheet 2 Arron/45y l atentecl Jan. 5, 1 954 PREHEATER ANDVAPORIZER FOR GAS TURBINE ENGINES Walter B. Whitelaw, Toronto, Ontario,Canada, assignor to A. V. Roe Canada Limited, Malton, Ontario, Canada, acorporation Application June 24, 1950, Serial No. 170,087

9 Claims. (Cl. 60-39371) This invention pertains to combustion chambersfor gas turbine engines and particularly to combustion chambers of thefuel preheating and vapourizing type.

In such engines, a high pressure and high velocity air stream is forcedby a compressor into an elongated combustion chamber, in which a lineror flame tube is mounted in spaced relationship to the casing of thecombustion chamber. Part of the air flows over the outside of the flametube between the flame tube and the casing of the combustion chamber andthe remainder flows longitudinally through it. Combustion occursprimarily in a region known as the flame zone contained within the flametube and it extends downstream, the combustion mixture beingprogressively diluted by air introduced from the outside of the flametube to provide a Working medium for a turbine.

Fuel may be introduced into the flame tubes of combustion chambers ofgas turbine engines by means of an atomizing spray, or in the form of avapour, or by a combination of atomization and vapourization.

In known constructions vapourization is effected by preheating theliquid fuel, either alone or in the presence of a limited supply of air,before admission into the flame zone, and this'is achieved by means ofvapourizing tubes through which the fuel is passed and which extenddirectly into the flame zone in a downstream direction; the tubes, aftertraversing the upper portion of the flame zone, are bent back uponthemselves to direct the vapourized fuel or a mixture of air andVapourized fuel upstream into the flame zone. Such vapourizing tubes areentirely dependent for their support on their mounting in a tube plateat the upstream end of the flame tube, an arrangement which isstructurally undesirable. Furthermore, particularly in instances whereair is introduced into the vapourizing tubes, it has been founddiflicult to distribute the fuel evenly over the internal surface of thetubes, especially at the bends therein; when there is unevendistribution of the fuel the normal cooling effect derived from thevapourization of the fuel is inadequate. The local overheating whichresults from this condition has caused many tube failures. It will beunderstood that failure of the tubes from any cause may result in piecesof the tubes being carried downstream seriously to damage the turbine.

Another shortcoming of known fuel systems is the limitation which theyimpose upon the choice of fuel. Although gas turbine engines are welladapted for operation using a Wide variety of fuels, the choice of fuelis usually restricted by the capabilities of the burners, vapourizersand the like which, when designed to produce satisfactory vapourizationof one type of fuel, e. g. kerosene, are often quite unsuited for usewith fuels of widely different characteristics.

The principal object of the present invention is to provide an improvedconstruction of combustion chamber for a gas turbine engine which willbe free from failure of the fuel vapourizing means due to fatigue,excessive local heating, or like causes. Another object of the inventionis to provide a fuel system which is suitable for use with a widevariety of liquid fuels ranging from gasoline to heavy fuel oils.

According to the present invention these objects are achieved by aconstruction in which fuel before admixture with the combustion air ispassed through a preheating element having a wall exposed to the flamezone and a wall re mote from the flame zone. Such a preheating elementmay extend over the entire surface of the flame tube containing theflame zone and thereby possesses the advantage of a much larger heatexchanging area than that furnished by the aforementioned prior art bentvapourizing tubes, permitting operation at lower overall temperatures toheat the fuel to the same extent. This in turn permits the use ofheavier and less costly fuels.

For the heavier fuels, means may also be provided in accordance with theinvention for superheating the fuel. For this purpose, after passagethrough the preheating. element, the fuel is passed through superheatingtubes disposed in the flame zone adjacent to the exposed wall of thepreheating element. Unlike the known vapourizer tubes, the preheatingtubes in accordance with the present invention may be adequatelysupported throughout their length, do not include any bends, and do notrequire to be disposed centrally in the hottest part of the flame zone.

To facilitate further the combustion of heavier fuels, in accordancewith a further feature of the invention, the fuel on emergence into aflame tube may be forcibly sprayed upon an impingement or splash memberdisposed in the high velocity airstream entering the flame tube from thecompressor.

Thus a construction in accordance with the invention eliminates the needfor the aforementioned bent vapourizer tubes extending substantially asunsupported cantilevers into the flame 3 zone, thereby obviating thedangers of tube failure due to fatigue or overheating, and it providesinstead a robust vapourizing device operating at relatively lowtemperatures.

In order that the invention may be more readily understood and carriedinto effect, some embodiments thereof will now be described withreference to the accompanying drawings, in which like referencecharacters refer to like parts in the several views and in which Figure1 is an elevation, partly in section; of a gas turbine engine embodyinga plurality of tubular combustion chambers constructed in accordancewith the present invention; v

Figure 2 is an enlarged section of the front portion of one of thetubular combustion chambers;

Figure 3 is a further enlarged section of 'a detail of Figure 2; and

Figure 4 is a section of an annular combustion chamber constructed inaccordance with the invention. V r V In the operationof the engineillustrated in Figure 1, air is compressed in a compressor It and fedthrough a difiuser H into a plurality of tubular combustion chambers l2,arranged in spaced relationship around a backbone member 93 of theengine. Fuel is injected into the combustion chambers l2 and burntin aportion of the available air, and the roducts of combustion and heatedair are discharged at high velocity into a turbine Hi, which drives thesaid compressor 5 t and, according to the construction of the turbineit, otherwise generates power from the energy contained in the hotgases. The final discharge of the gases from an exhaust i5 may beemployed for jet propulsion of the unit. (The relative location of thevarious parts is herein referred to as upstream or downstream withrespect to the sense of the air flow through the engine.) I 7 As shownmore clearly in Figure 2, eachtubular combustion chamber :2 has an outercasing l2 'and a flame tube it secured coaxially therein by means of asupport it and also by suitable mountings for interconnectors [8, whichconstitute ports for the connection of neighbouring combustion chambers.p H U The upstream or inlet portions of the combustion chamber casing l2and of the flame tube i6, surrounding the fiame zone l9, decrease indiameter toward the air inlet, being substantially conical in shape. Airfrom the compressor Iii is forced into the upstream end of thecombustion chamber 22 in the direction of the arrowA (see Figure 2). Aportion of the air enters the flame tube it and the remainder passesbetween the flame tube is and the combustion chamber casing i2 coolingthe flame tube and in part being introduced into the flame tubedownstream of the flame zone through apertures (not shown) in the flametube, to provide the workingfluid for the turbine i i to which thecombustion chamber discharges.

In the embodiment of the present invention illustrated in Figures 1 to3, fuel is introduced to the combustion chamber 52 at the forward end bya conduit 28, one end of whichcommunh cates with a source of fuel underpressure and the other end of which communicates with an annularpreheating element 2!, providing a chamber 25* which extends along thesurface of the upstream portion of the flame tube is; the wall of theflame tube i6 itself provides the'out er or remote wall of the saidannular preheating ele 4 ment, and the inner or exposed wall 2| of thepreheating element 2| constitutes an annular liner which is exposed tothe flame zone and in direct contact with the hot gases therein. Thepreheating chamber 2 F is closed at its upstream end and terminates atits downstream and in a somewhat enlarged portion providing a hollowrear distributing ring 22. Extending upstream from the distributing ring22 is a plurality of spaced, symmetrically disposed, superheating tubes23 which lie in the flame zone adjacent to and supported by the exposedwall 2 l of the preheating element. The superheating tubes terminate ina hollow front distributing ring 2% located concentrically to andadjacent the upstream end of the preheating element in te flame tube. Inthe front distributing ring 25 is provided a series of spaced apertures25 directed downstream and designed to operate as spray nozzles (seeFigure 3).

Inside the upstream end of the flame tube 16 and spaced from the frontdistributing ring and the superheating tubes 23 in an deflector 2'3,comprising a hollow truncated conical member terminating downstream insharp circular edge 26? and a plate 2? extending transversely across thedeflectorfzft; a peripheral flange 27 on the plate 2'. is secured to theinside of the conical member. The conical surface of the air deflector2b is arranged substantially parallel to the conical upstream portion ofthe wall of the flame tube l8, and the front edge 2t of the airdeflector is substantially flush with the upstream end of the flametube,while its rear edge extends downstream to a hypothetical planelocated approximately one-quarter to one-third of the distance from thefront distributing ring it to the rear distributing ring 22. V The plate2? lies in a radial plane situated a short distance upstream of the rearedge of the deflector 25. The flame zone I 9 is situated immediatelydownstream of the air deflector 2t and the plate 2'! may advantageouslyhave one or more apertures 2? to admit additional air through the plateinto the flame zone. H v Surrounding the central portion of the conicalair deflector 26 and supported in parallel spaced relationship to thedeflector is impingement member 28 which in effect is a second truncatedcone of slightly larger diameter.

In operation, fuel in liquid form and under pressure enters thepreheating chamber Zi as previously described, and flows through to therear'distributing ring 22. As the fuel flows downstream through thepreheating chamber 25 it receives a considerable amount of heat sinceone wall of the surrounding preheating element is exposed to radiationfrom the flame zone it". From the rear distributing ring 22 the heatedfuel travels upstream again through the series of superheating tubes 23and in so doing it absorbs more heat, becoming very hot by the time itreaches the front distributing ring 24.

Air from the compressor is enters the com bustion chamber l2 at theupstream end in the direction of the arrow A and a portion of the airenters the flame tube it while the remainder passes between the flametube 16 and the combustion chamber casing E2? The portionof air enteringthe flame tube it is guided by the air deflector 26 so that it passesbetween the deflector and the flame tube. The area of low pressure inthe airstream created immediately downstream of the plateE'i'establishes a region of relative stability in the flame zone l9,into which some air may be admitted directly, if desired, by providingthe previously mentioned optional apertures Zl in the plate 21.

The very hot fuel emerging at high velocity from the nozzle 25 strikesthe conical impingement member 28 and breaks into a fine spray or vapourdue to the combined effect of its high temperature and the mixing actionof the high velocity air passing on both sides of the impingementmember. Any fuel which is not vapourized upon leaving the impingementmember 28 strikes the outer surface of the air deflector Z6 and isfinally swept off the sharp rear edge of the air deflector 26 in theform of a vapour or a fine spray. The mixture of air, fuel vapour and,in lesser amount, fine droplets of fuel, enters the flame zone isimmediately downstream of the air deflector 26.

The aforementioned embodiment of the invention is particularly adaptedfor operation with. heavier fuels. If lighter fuels only are to be usedin the combustion chamber then the superheating' tubes 23 may bedispensed with and the rear distributing ring serves as an inlet channelfor the preheating chamber Zi In this instance the conduit 25] isconnected to the preheating chamber 25* at the downstream end of thelatter to introduce the fuel directly in the rear distrib-uting ring 22the fuel flows upstream through the preheater chamber Zi which isarranged to communicate at the upstream end with a front distributingring similar to the aforedescribed ring 2t, from which the fuel is thenejected into the flame zone H! by nozzles similar to the nozzleapertures 25. Furthermore, when using some of the lighter fuelsefficient combustion may be obtained without incorporating animpingement member 23. However it should be understood that aninstallation embodying both the superheating tubes and the impingementmember may be used satisfactorily with lighter fuels and the provisionof these features imparts some degree of flexibility in the choice offuel.

The preheating element containing the chamber 2| has been described andillustrated as being provided by a wall spaced from the flame tube andexposed to the flame zone, but it will be appreciated that alternativelythe element could be provided by a wall spaced from the flame tube andremote from the flame zone. In the latter case, the flame tube itselfwould provide the exposed wall of the preheater element.

In the application of the invention to a combustion chamber 29 ofannular form, as illus trated in Figure 4, it is to be understood thatthe annular combustion chamber'29 simply takes the place of theplurality of combustion chambers i2 illustrated in Figure 1, thearrangement being otherwise similar. The annular combustion chamber 29is mounted coaxially with the backbone member [3 of the engine and issupplied with compressed air from the diffuser H, the hot gases beingdischarged into the turbine It.

By reference to Figure 4, it will be seen that the combustion chamber 29comprises an annular chamber bounded by an inner casing 39 and an outercasing 3! mounted coaxially with the backbone member is of the engine.Between the casings so and 3! is the flame tube provided by the innerwall 32 and the outer wall 33; these walls 32 and 33 are supported inspaced relationship to the casings 3i! and 3| of the combustion chamberso that annular spaces 1M and. 35 are provided between the inner wall ofthe flame tube 6 and the inner casing of the combustion chamber andbetween the outer wall of the flame tube and the outercasing of thecombustion chamber respectively.

In this construction, according to the invention a hollow annular casing36 forming the upstream portion of the wall 32 of the flame tubecontains an annular preheating chamber 36. The casing 36 has at itsdownstream end an enlarged portion constituting a rear distributing ring3? located where the casing 3t abuts the flame tube wall 32. Liquid fuelis supplied under pressure to the upstream end of the preheating chamber36 by means of conduit 38, the construction being such as to favour aneven distribution of fuel in the preheating chamber 36. The fuel flowsto the rear distributing ring 3'! at the downstream end of thepreheating chamber, and from the ring the fuel passes through a seriesof superheating tubes 39 to a front distributing ring 46 provided with aseries of spaced spray nozzles similar to the nozzles 25 (see Figure 3)the general features of construction are similar to those described inconnection with the application of the invention to one of a pluralityof tubular combustion chambers.

An impingement member M comprising a narrow ring of truncated conicalform and a larger diameter than the inner wall 32 of the flame tube isprovided; the impingement member is disposed adjacent the spray nozzlesand parallel with and spaced from the said wall of the flame tube so asto present an oblique surface to fuel ejected from the nozzles. An airdeflector 62 is also mounted within the forward portion of the flametube and comprises a truncated conical member coaxially encircling andspaced from the impingement member 4! and disposed in a plane parallelto the surfaces of the impingement member and of the inner wall 32 ofthe flame tube. An annular plate 43 lying substantially in a radialplane of the engine is situated a short distance upstream of thedownstream edge of the deflector 42 and extends between the airdeflector at its inner radius and the outer wall of the flame tube atits outer radius. The plate 13 may be provided with a number ofapertures to permit the entry of some air through the plate into theflame zone 44 which is situated immediately downstream, as describedwith respect to the applica tion of the invention to a tubularcombustion chamber.

The airstream from the compressor It enters the combustion chamber 29 inthe direction of the arrows B in Figure 4. Part of this air passes overthe inner and outer surfaces, respectively, of the inner and outer walls32 and 33 of the flame tube to cool the said flame tube and to providediluent air, and the other portion of the air passes through the flametube to support combustion. The main air for combustion flows throughthe annular space provided between the conical surface of the airdeflector t2 and. the inner wall 32 of the flame tube, passing on bothsides of the impingement member il. The functioning of this combustionchamber is similar to that previously described in relation to thetubular combustion chamber and should be clear without furtherexplanation.

t is to be understood that the details of the construction of theaforedescribed embodiments of the invention may be modified withoutexceeding the scope of the invention. For example in the case of theannular combustion chamber, it

will be realized that the preheating chamber could alternatively beprovided in the outer'wall 33 of the flame tube, a correspondingrearrangement of the impingement member and the air deflector beingmade, when such parts are used. Furthermore the preheating elementcontaining the chamber 36 may be provided by a wall spaced from theflame tube and either exposed to'the flame zone or alternatively remotefrom the flame zone; in the latter construction the flame tube itselfconstitutes the exposed wall of the preheating element. Furthermore ineither construction the preheating chamber may extend over the surfaceof the flame tube to a greater or lesser degree than that shown in thedrawings or a configuration of the air deflector may be adopted whichwould render the radially disposed plate unnecessary in creating thestabilizing depression in the flame zone; and the proportions andarrangements of the various other elements may be modified to suit theconstruction of-the engine.

The term remote as. used herein and inthe subjoined claims in referenceto a wall of the preheating element is not to be read as meaning thatthe said wall is situated at a great distance from the flame zone;actually the element itself is of relatively narrow crosss-section. Theterm is used to signify that the wall isnot exposed to the flame zone,as distinct from the other wall of the element which is so exposed.

What I claim as my invention is:

1. A vapourizing system for a .gas turbine engine comprising, a flametube having anopen end for the admission of air and containinga flamezone of primary combustion, a preheating element having a wall facingthe interior of the flame tube and being exposed to the flame zone andhaving another wall spaced from the said exposed wall and being remotefromthe flame zone, a fuel conduit communicating with the .preheatingelement for introducing liquid fuel between the walls of the preheatingelement to preheat the fuel, superheating tubes situated in the flamezone and disposed adjacent the 56X- posed wall of thepreheating'element, :the superheating tubes communicating with thepreheating element to receive the preheated fuel, .discharging meanscommunicating with the superheating tubes for discharging thesuperheated fuel into the flame tube, and means 'deflectively interposedin the path of discharge of the discharging means and exposed to thestream of air to scatter the superheated fuel in the air stream.

2. A vapourizing system for a gas turbine-engine comprising, a flametube-havinga-n open end for the admission of a stream of air ,andcontaining a flame zone of primary combustion, a preheating elementhaving a wall facing the interior of the flame tube and being exposed tothe flame zone and having another wall spaced from. the said exposedwall and being remote from the flame zone, a fuel conduit communicatingwith the preheating element for introducing liquid fuel between thewalls of the preheating element to preheat the fuel, superheating tubessituated in the flamezone anddisposed adjacent the exposed wall of thepreheating :element, the superheating tubes being supported by theexposed wall of the preheating element and communicating with thepreheating-element to receive the preheated fuel, discharging meanscommunicating with the superheating tubes for discharging thesuperheated fuel into the flame tube, and means deflectively interposedin the pat-h of discharge of the discharging means and exposed to thestream of air to scatter the superheated fuel in the air stream.

3. A vapourizing system for-a gas turbine engine comprising, a flametube having an open end for the admission of a stream of air andcontaining a flame zone of primary combustion, a preheating elementhaving a wall facing the interior of the flame tube and being exposed tothe flame zone and having another wall remote from the flame zone, thepreheating element having an upstream end adjacent the open end of theflame tube and a downstream end, a fuel conduit communicating with theupstream end of the preheating element for introducing liquid fuelbetween the walls of the preheating element to preheat the fuel,superheating tubes situated in the flame zone and disposed adjacent theexposed wall of the preheating element, the superheating tubescommunicating with the downstream end of the preheating element,discharging means communicating with the superheating tubes fordischarging the preheated and superheated fuel into the flame tube, anda spray-producing member deflectively interposed in the path ofdischarge of the discharging means and exposed to the stream of air andthe discharged fuel to scatter the preheated and super.- heated fuel inthe air stream.

4. A vapourizing system for a gas turbine engine comprising. a flametube having an open end for the admission of a stream of air andcontaining a flame zone of primary combustion, a preheating elementhaving a wall facing the interior of the flame tube and being exposed tothe flame zone and having another wall spaced from the said exposed walland being remote from the flame zone, the preheating element having anupstream end adjacent the open end of the flame tube and adownstreamend, a fuel conduit communicating with the upstream end of thepreheatingelement for introducing the liquid fuel between the walls of thepreheating element to preheat the fuel, superheating tubes situated inthe flame zone and disposed adjacent to :the exposed wailof thepreheating element, the superheating tubes communicating with thedownstream end of the preheating .element and extending toward theupstream end thereof, a distributor communicating with the upstream endsof the superheating tubes and being provided with nozzles .adjacent theopen end of the flame tube for discharging the preheated and superheatedfuel into :the flame .tube, and means deflectively interposed in thepath of discharge of the nozzle and exposedto the stream of air toscatter the preheated and superheated fuel in the air'stream.

5. A vapourizing system for a gasyturbine engine comprising, a flametubelhaving an open end for the admission of a stream of air andcontaining a flame zone of primarycombustion, a preheating elementhaving a wall. facing the interior of the flame tube and :being exposedto the flame zone and having another wall spaced from the saidexposedwall and being remote from the flame zone, the preheating element havingan upstream end adjacent the'open end of the flame tube and a downstreamend, a fuel conduit communicating with the upstream end of thepreheating element for introducing liquid fuel between the walls'of thepreheating element topreheat the fuel before admixture with air,superheating tubes communicating with the downstream-end of thepreheating element and disposed adjacent the exposed wall of thepreheating element, an impingement member situated in the open end ofthe flame tube and in spaced relationship with the flame tube, theimpingement member being exposed to the stream of air, and a distributorcommunicating with the superheating tubes and provided with nozzlesdirected toward the impingement member for spraying the preheated andsuperheated fuel forcibly against the impingement member to scatter thepreheated and superheated fuel in the air stream.

6. A vapouring system for a gas turbine engine comprising, a flame tubehaving an opening for the admission of a stream of air, an impingementmember having a frusto-conical outer surface disposed in the openingwith its base end directed downstream with respect to the air stream, asource of fuel, and a ring of discharge outlets each connected to thesource of fuel, the surface of the impingement member intersecting theaxis of flow of each of the outlets whereby fuel discharged from theoutlets may be scattered in the air stream on contact with theimpingernent member.

7. A vapourizing system or a gas turbine engine comprising, a flame tubehaving an opening for the admission of a stream of air, a fuel atomizerincluding a deflector disposed in the opening and having afrusto-conical outer surface the base end of which is directeddownstream with respect to the air stream, and an impingement memberencircling and spaced from the said surface, a source of fuel, and aring of discharge nozzles each connected to the source of fuel and beingso positioned in relation to the position of the impingement member thatthe paths of discharge of the nozzles is intersected by the outersurface of the impingement member for spraying the fuel forcibly againstthe impingement member to scatter the fuel in the air stream.

8. A vapourizing system for a gas turbine engine comprising, a flametube having an opening for the admission of a steam of air, a fuelatomizer including a hollow open-ended deflector disposed in the openinghaving a frusto-conical outer wall surface the base end of which isdirected downstream with respect to the air stream, the fuel atomizeralso including a baiiie disposed transversely in the deflector to createa low pressure space in the flame tube downstream of the baffle and animpingement member hav ing a frusto-conical outer Wall surface coaxiallyencircling and spaced from the said surface in substantially parallelrelationship thereto, a source of fuel, and a ring of discharge nozzleseach connected to the source of fuel and being so positioned in relationto the position of the impingement member that the paths of discharge ofthe nozzles is intersected by the outer surface of the impingementmember for spraying the fuel forcibly against the impingement member toscatter the fuel in the air stream.

9. A vapourizing system for a gas turbine engine comprising, a flametube wall encircling a flame zone and providing an opening for admittinga stream of air to the flame zone, an outer wall spaced from the firstwall and providing between the walls an annular liquid fuel preheatingspace of appreciable axial length, a conduit leading to one end of thesaid space for introducing liquid fuel, fuel discharge nozzlesconimunicating with the other end of the said space, and a bafliedisposed in the opening and deflec tively interposed in the path ofdischarge of the nozzles to scatter the fuel in the air stream.

WALTER B. WHITELAW.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,030,843 Dunham et a1 June 25, 1912 1,405,482 Bostedo Feb. 7,1922 1,920,124 Gillis July 25, 1933 2,404,335 Whittle July 16, 19452,443,707 Korsgren June 22, 1948 2,552,851 Gist May 15, 1951 2,622,396Clarke Dec. 23, 1952

